31 thoughts on “Stratolaunch”

As others comment at the Berger article, it’s hard to tell if the math works. You don’t win as much dV as you’ld think with air launch, but maybe you could close the gap enough to get a small payload to orbit, maybe with a small expendable kicker stage. Could also be an inefficient but low-G way to launch fragile cargo (e.g. non-astronaut humans). YMMV.

Stratolaunch can supposedly lift 250t to altitude and therefore has the same lift capacity as the An-225 used by Interim-HOTOL, which was a single-stage pure-rocket design that could put a 7t payload into LEO. Going to a two-stage rocket would likely increase this performance past 10t and would be quite a useful capability, especially if it could support daily flights to LEO.

Sorry should have included this in my reply. From source cited previously:
Gross lift off (or drop) weight is expected to be over 465,000 lb, with the air launch vehicle (Pegasus-II) able to deliver 13,500 lb to LEO, or 9,900 lb to a highly inclined (HIO) orbit, or 4,500 lb to GTO.

Rand, I would presume the GLOW limits to the carrier aircraft remain regardless of payload. Whether that be a Pegasus-II or something else. Maybe Stratolaunch is fishing for a supplier, but the carrier aircraft was designed with some type of base-line in mind. Pegasus-II is it, after SpaceX bowed out.

The carrier aircraft has a PL capacity of 250 tons, from the various air launch concepts I’ve give the payload the carrier aircraft can handle using kerosene/LOX propellant would make up 90% of the spaceplanes wet mass, so with spaceplane structure + PL around 25 tons, PL might be around 5 tons.

Air launch has the advantage of being able to get to any particular orbit at short notice compared to ground launch.

Maybe someone who’s better with the math than I am can explain how this is helpful. Is it kind of an X-15 scenario? Is it about reducing drag, or optimizing the spaceplane for high-altitude aerodynamics?

I get the bit about orbit flexibility, I suppose; fly to a good launch position. And I guess it helps with weather, since you’d be above most of it. But it’s the overall efficiency I’m not sure of. It seems like it’s not much help.

Because of how the rocket equation works in practice even a little bit of help in lowering the required delta v can make a big difference in the mass ratios, in principle substantially increasing the payload size.

Dan Delong had an 747 air-launched SSTO RLV concept that I reviewed on Selenian Boondocks about a decade ago. I can’t remember exact details, but I think it was in a similar GTOW class as what Roc can handle, and used LOX/LH2 propellants, to enable something like a 14klb to LEO (~6mT) payload. Which is actually a pretty nice payload range if it’s highly reusable. There’s some definite technology updates I would consider these days, but there are far worse launch vehicles he could develop for Roc than a fully-reusable stage.

Even with efficiencies of scale, and efficiencies of staging, my guess is that a fully-reusable airlaunched SSTO like this could be a lot cheaper in $/kg than a partially reusable Falcon 9 or Falcon Heavy for instance.

I actually kind of like the idea, though I don’t really have time to write about it this week.

Jon after reflection on your article from 1/4/2008 and to be fair in light of recent reveals from Musk ala the BFS, I’m inclined to think these days that perhaps a two modal engine design around a common propellant housed in the fuselage might be preferable to TAN and wet wing tanks. Since big round composite tanks are a solved problem (for some function f(n) of space access providers (read SpaceX). By two modal I mean one or one set of engines for in atmosphere operation and one or one set of engines for vacuum op ala BFS. If you add wings with control surfaces and an RCS for orbital ops you probably don’t need to gimbal them which helps.

Just pointing out things have changed a lot since 2008. And have added some wrinkles that weren’t under consideration in 2008 that in the subsequent 10 years time might be. Also in light of the methalox approaches maybe less emphasis on LH2 which would help in tankage (cryogenics), density and fuselage diameter (drag). But for 2008 you have a great reference there Jon. Thanks!

Second stage of Saturn V had gross mass of 480,000 kg. And mass of LOX was 357,882 kg or without
LOX it’s gross is 123 tons.
So have vehicle that can land with empty rocket fuel and has gross mass of about 400 ton, uses LH2 and
LOX,takeoff with less LOX. Fill up LOX in flight.
Takeoff mother ship with 25% jet fuel- in flight fuel with jet fuel. Have extra rocket LOX in mothership transfered from Mothership to rocket in flight.
And abort options would dump LOX.
So mothership has capability to dump or transfer LOX and it’s about 100 tons of LOX. And air tanker adds about 150 tons of jet fuel to mothership.

From what I remember this was supposed to be the Tier 2 launch platform (i.e. the orbital successor of SpaceShipOne). But it seems to be a vehicle in search of a mission really. I mean it doesn’t have an actual space launch vehicle nor are there any mentions of a possible payload. I’ve never been a fan of the air launch concept with jet engines really. Any horizontal launch vehicle will lose performance. He have a hard enough time with the vertical launch margins as it is.

At the end of the day, even SpaceX’s BFR will be at the mercy of the range. It will have to deal with the weather hand it is dealt. And, as a fixed point, it has zero flexibility with regard to orbital phasing.

The general Stratolaunch concept is intriguing, but we need to see the details on the rocket side.

I’ve never really understood the idea of “the range”; maybe someone could explain it? Obviously a crashing spacecraft is unlikely to hit anything important, and obviously there’s a small chance it will. That sounds about the same as an airplane to me, but we let aircraft take off whenever and hope for the best; usually we prefer that the takeoff is away from major populated areas.

Something else I’ve wondered about: Stratolaunch has a range of about 1,100 miles. (According to Wikipedia.) (Also, screw the metric system.) Assuming that’s “loaded out, empty in”; i.e. taking off with a payload and returning after launch, that means that by going due south, Stratolaunch can go about 2/3 of the way down Baja California before they get uncomfortably close to “No Return” if they want to land at Mojave. This won’t be a factor for polar orbits but for the more valuable equatorial orbits, it’s just barely south of Cape Canaveral. Also, what do Mexico, Guatemala, and the other LA countries think of launching rockets over their territory?

The more I think about this approach (Stratolaunch) in light of current rocket based approaches the more and more Spruce Goose is looking like a good analogy.

On paper Stratolaunch looks like it ought to be a great way to deliver payload through the orbital goal posts. The problem is SpaceX with their reusable fly-back booster have mounted the goal posts on wheels.

Assuming SpaceX is truly able to achieve gas-and-go with the bulk of operations being RTLS it’s hard to see any clear advantage. That leaves small payload ops. But there’s Electron and guys like that. Henry Spencer has said for a long time that in the long run it will be far cheaper for smallsats to just piggyback off F9 or BFR launches.

That leaves Stratolaunch using birdzilla mainly to transport semi-tractor based cargo containers using fairings and end caps across country, with orbital work on the side. But with only one instance that’s a pretty limited market. I’m thinking rock concert support? Am I off base here in 2018?

A reusable space-plane could be a first step at a crewed vehicle orbital option ala next gen Virgin Galactic. But the barrier to entry is so high, Stratolaunch is not positioned for that kind of certification. A solution in search of a problem?

One more reflection: from Jon’s analogy by cheating to solve the SSTO problem by using an airbreather to replace the first stage, Stratolaunch has landed squarely on the big problem that even SpaceX hasn’t solved yet and won’t solve until BFS. And that is how to reuse the second stage!

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